300SE stumble at idle

The 300SE had a severe stumble at idle.   It only occurred when the engine was hot.  It never stalled the engine, but felt like it was about to.    There was also a miss at takeoff.    My initial thought was to check the distributor cap and rotor.   However,  on further examination, you could see sparking around the #6 spark plug.   It appeared that the miss was probably related to the damaged insulation on the suppressor.

The suppressors are available for purchase separately and just screw off.   I was given a tip on the forums to use a Stanley knife to cut away the insulation and squirt some WD40 on the thread to make sure the end of the wire is not damaged.    Once I started to cut the insulation, it became obvious that the damage was more than just skin deep, the plastic insulation was also badly cracked.

This was obviously how the spark was getting out.      While #6 was the worst, the others look fairly old and may be worth changing.

The car now runs much better.  The stumble seems to be gone and there is more power.   Not surprising since it wasn’t really running on all 6.  I will still check the cap and rotor as the idle is not perfect, and I do not know how old they are.